This application claims priority on Finnish Application No. 20000873, Filed Apr. 12, 2000, the disclosure of which is incorporated by reference herein.
Not applicable
The invention relates to a method for measuring slide bearing pressure in a deflection-compensated roll with a fixed shell.
In paper and board machines, deflection-compensated rolls (TK) are in general used which are formed from a stationary support structure and a tubular shell arranged to rotate therearound, said shell being bearably carried on the ends to a support structure by end bearings. Between the shell and the support structure, hydraulically loaded loading elements are moreover provided, being supported to the support structure and acting on the inner face of the shell in a radial direction, wherewith the profile of the shell can be adjusted in the axial direction. A row of loading elements to be used for adjusting the profile of the shell is positioned in the nip plane and with said loading elements, the bending of the shell of the TK roll and the backing roll is compensated so that the force acting on the web in the nip plane is equal across the entire axial direction of the shell. To intensify the profiling, so-called loading elements forming a counterzone can in addition be used on the opposite side of the support structure in relation to the nip in the TK roll. The loading elements of the counterzone can be positioned in one row, whereby a row is in the nip plane, or in two rows, whereby the rows are located symmetrically on both sides of the nip plane. By means of the loading members of the counterzone the shell can also be loaded with a desired force, whereby the configuration of the shell is profiled to be as desired.
The TK rolls can be divided into rolls with a mobile shell and rolls with a fixed shell. In the present context the TK rolls with a mobile shell refer to rolls in which the end bearings can be moved in radial direction, that is, normally in the nip plane relative to the support structure, whereby also the shell moves together with the end bearings in the nip plane. Transferring of end bearings is normally carried out so that pressure spaces acting in the nip plane are arranged between the end bearings and the support structure. By conducting a pressure medium into said pressure spaces, the end bearings can be transferred in the nip plane. By means of said transfer of the end bearings relative to the support structure, the opening and closing of the nip can be carried out, as well as partial loading and relief of the TK roll against the backing roll.
The TK rolls with a fixed shell refer to rolls in which the shell is not, at least to a significant extent, moved in a radial direction relative to the support structure. On fixed-shell TK rolls, the opening and closing of the nip and the loading and relief of the TK roll against the backing roll are performed with hydraulically operating loading arms supported to the support structure of the TK roll. In fixed-shell rolls, mechanical rolling bearings or hydraulic slide bearings can be used as end bearings. In a fixed-shell roll provided with rolling bearings, the end bearings are locked in radial direction to the support structure and the shell is locked in radial direction to the end bearings. In a fixed-shell roll provided with hydraulic slide bearings, the shell is able to move slightly in a radial direction owing to the nature of the bearing.
In rolls with a mobile shell and a fixed shell, rolling bearings or slide bearings can be used for end bearings between the shell and the support structure.
The present invention can be embodied in fixed-shell TK rolls provided with hydraulic slide bearings, in which the slide bearing operation is carried out essentially without strokes.
In FI patent No. 76870 (Kleinewefers GmbH), a TK roll with a fixed shell is disclosed, in which the shell is bearably carried on the ends of a support structure with rolling bearings. Indicators are arranged in the area of the rolling bearings, the measurement values of which indicate loading of the end bearings in the nip plane. By means of a control device, pressures to be supplied to the loading shoes of the loading zone and the loading shoes of the backing zone are controlled, being dependent on parameters measured in operation and/or determined in advance, and depending on the measurements of the indicators so that the loading of the end bearings is approximately zero in the nip plane.
Instead of measuring the direct bearing force with the aid of indicators arranged in the area of the rolling bearings, the forces acting on the rolling bearings can be defined also indirectly. This can be carried out by measuring the forces acting on the support spots of the support structure of the backing roll, the forces acting on the support spots of the support structure of the TK roll and the forces caused by the loading devices on the shell of the TK roll. On the basis of said forces, the forces acting on the rolling bearings of the TK roll are calculated. In the loading spots in which the forces are generated with the hydraulic loading devices, the pressures of the hydraulic loading devices are measured and on the basis thereof and of the surface areas of the pressure chambers of the pistons of the hydraulic loading devices, the forces acting on the hydraulic loading devices are calculated. In the calculations, the masses acting in the support spots and the friction factors acting in different locations are moreover paid attention to. The bearing force calculated with this kind of method is naturally inaccurate.
FI patent No. 79177 discloses a deflection-compensated roll with a mobile shell provided with rolling bearings. Therein, the shell is bearably carried on both ends to the support structure with rolling bearings arranged on top of the annular parts. Between the annular parts and the support structure, hydraulic loading members are disposed. With the loading members, the shell can be transferred relative to the support structure for opening and closing the nip. By the loading members, the shell can also be loaded against the backing roll.
In the mobile-shell TK rolls, in which a transfer of the end bearings based on the rolling bearings is carried out with a hydraulics medium brought into the pressure spaces between the bearings and the support structure, the pressure of the pressure medium conducted into said pressure spaces can be measured. A certain nip profile requires the use of a bearing force of a given magnitude, whereby the pressure equivalent thereto is tried to be kept under the bearing. The bearing force is determined on the basis of the surface areas of the pressure spaces influencing the bearings.
With the method according to the invention, sufficiently precise information is achieved each time of the pressures acting on the slide bearings of the fixed-shell TK roll being carried with slide bearings, on the basis whereof the forces acting on the slide bearings can be calculated.
The slide bearing of a TK roll comprises main bearing elements acting in opposite directions in the nip plane and side bearing elements acting in a transverse direction relative to the nip plane. Immediately below the first main bearing element focussed on the nip, that is, the guiding main bearing element, a first control valve is positioned, which on the basis of the loading acting on the main bearing elements distributes the pressure medium between the main bearing elements. To that main bearing element on which a greater load is at each moment acting, a greater flow and pressure is fed and respectively, to an opposite main bearing element, a lesser flow and pressure is fed. The control of the side bearing elements is carried out in an equivalent manner with the aid of a second control valve. The control valves should be located right below the guiding bearing element so that their response to an external loading can be made as brief as possible.
The invention is described below in detail, referring to the example embodiments of the invention presented in the figures of the accompanying drawings, whereto the invention is not intended to be solely restricted.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.